Optically pumped magnetometers (OPMs), also called atomic magnetometers, optical magnetometers, or optical atomic magnetometers, are used in a number of scientific and advanced technology applications including medical imaging. In their simplest form, they contain a light source, a container to hold atoms, and a detector. The light source may be a laser or other optical device used to produce light of a certain wavelength. The container may be a vapor cell or other device used to house atoms. The detector would necessarily be specific to the light output.
Single OPMs or small arrays of OPMs have been used routinely to create magnetic field images or gradient magnetic field images and to localize magnetic sources. In many cases, the sensors or sensor arrays are mounted onto moving platforms and moved in regular patterns over the area of interest. Alternatively, larger arrays allow the sensors to be stationary. In order to localize magnetic sources, the positions of the sensors have to be known. For large area images, the sensor location can be determined with global navigation satellite systems (GNSS), such as but not limited to the global positioning system (GPS). For smaller areas of interest, sensor positions have been determined geometrically or optically. For some OPMs, an additional complication comes from the fact that the position at which the magnetic field is measured is determined by the position of the laser beam, not a physical component of the sensor.
There are several other factors that determine the quality of the image and the source localization apart from the locations of the sensors in the array, such as but not limited to, sensor orientation, sensor gain as a function of frequency, sensor bandwidth, sensor cross-talk, and sensor linearity. All these sensor array parameters are usually calibrated at least once before the measurement.